About

Replacing old lighting fixtures with energy-efficient alternatives is one of the quickest ways to reduce electricity costs. However, watts (W) measure energy use, not brightness. To find the correct replacement bulb, one must calculate the wattage required to match the original luminous flux (Lumens). This calculation depends entirely on the "Luminous Efficacy" of the technology, measured in lumens per watt (lm/W).

This tool helps consumers and electricians bridge the gap between brightness and power. By selecting the bulb technology - from inefficient tungsten filaments to modern high-output LEDs - users can estimate the power draw needed to achieve a desired brightness. Accurate efficacy inputs ensure that the results reflect real-world hardware specifications.

Formulas

Power is derived by dividing the total light output by the efficacy ratio:

P = Φ_vη

Where:

P = Power in Watts (W)
Φ_v = Luminous Flux in Lumens (lm)
η = Luminous Efficacy (lm/W)

Reference Data

Technology	Typical Efficacy (lm/W)	Watts for 800 lm (approx)
Incandescent (Tungsten)	12 - 18	60 W
Halogen	15 - 25	45 W
CFL (Compact Fluorescent)	50 - 70	14 W
LED (Standard)	80 - 110	9 W
LED (High Efficacy)	120 - 170	6 W

Frequently Asked Questions

Luminous efficacy is a measure of how well a light source produces visible light from electricity. It is the ratio of luminous flux to power (lm/W). A higher number means the bulb is more efficient.

LED technology is improving rapidly. An older LED might produce 80 lumens per watt, while a new high-end industrial chip might produce 160 lumens per watt. This is why checking the specific packaging or datasheet is important.

Only for old incandescent bulbs. For an LED, 800 lumens is usually achieved with just 8 to 10 Watts. This misconception comes from years of associating "60W" with a specific brightness level.

Grow lights are often measured in PAR (Photosynthetically Active Radiation) or PPFD, not just Lumens. While Lumens measure light visible to the human eye, plants need specific wavelengths. This tool gives a general idea of power but isn't specific to plant biology.